This invention relates generally to projectile fuzes and more particularly to a device for selectively determining whether, upon projectile impact, detonation of the projectile explosive occurs instantaneously, i.e., point detonation (PD), or is delayed.
A PD/delay device is a combination of two functional assemblies, each embodying a number of mechanical elements. The selector assembly, through its mechanical elements, controls, either directly or indirectly, the functioning of the alignment assembly which contains the PD and delay detonators. Through the selector assembly the operator manually predetermines whether the projectile explosive will be exploded in the PD mode or the delay mode. During projectile flight the mechanical elements of each assembly cooperate among themselves, and interact between assemblies, under the influence of acceleration, centrifugal and mechanical forces, to align either the PD detonator or the delay detonator in the fuze explosive train.
As the number of mechanical elements of a PD/delay device increases, the fabrication cost of the device increases, the fabrication of the fuze body becomes more complex, the integration of the PD/delay device into the fuze body becomes more difficult, and the overall reliability of the fuze decreases. In addition, the greater the number of elements comprising a PD/delay device, the larger is the fuze body cavity required to house the device thus increasing the probability of a fuze malfunction due to the impact deformation forces transmitted through the fuze body, i.e., the hard target penetration capability of the warhead is reduced.
The current fuze for 76 mm, 3 inch/50 and 5 inch/54 naval guns is the MK 407 MOD 1. The PD/delay device for the MOD 1 has divergent-convergent channels that interface with the single axial firing passage. The delay detonator, positioned in one of the divergent-convergent channels, is always aligned in the fuze explosive train. The PD detonator, positioned in the other divergent-convergent channel, is disposed in a rotatable cylinder and is rotatable into or out of alignment with the fuze explosive train by means of a selector switch. Therefore the reaction energy generated by projectile impact always ignites the delay detonator. When the PD option is selected, the PD detonator is rotated into alignment in the fuze explosive train and is ignited by the reaction energy of projectile impact; since the reaction time of the PD detonator is nearly instantaneous the PD detonator reaction energy ignites the next relay element in the fuze explosive train rather than the reaction energy of the delay detonator. A major limitation of the MK 407 MOD 1 PD/delay device is that the exothermic reaction energy generated by projectile impact diverges as it enters the PD/delay device to transverse the divergent-convergent channels; this attenuation of the reaction energy increases the probability of misfire due to lack of sufficient energy to ignite the detonators in the PD/delay device. This device also requires exotic manufacturing techniques to fabricate the divergent-convergent channels which increases the cost and difficulty of manufacturing the fuze. The integration of the PD/delay device in the fuze body requires a larger internal cavity which decreases the hard target penetration capability of the warhead.
The selector assembly of U.S. Pat. No. 2,651,993 to Berzaf et al. directly controls the alignment assembly. The alignment assembly has two longitudinal grooves, of different lengths, connected by an arcuate groove. The pin of the selector assembly is initially disposed in the arcuate groove and may be rotated to either longitudinal groove depending upon which detonation option is selected. With the pin in the selected longitudinal groove the alignment assembly can translate under the action of a spring-bias force to align the selected detonator in the fuze explosive train. Three spring-biased safety mechanisms, two of which function under the influence of the setback force generated when the projectile is fired and one of which functions under the influence of the centrifugal force generated by the spin of the projectile during its free-flight trajectory, interact with the alignment assembly to preclude its translation prior to projectile firing.
In the PD/delay device described in U.S. Pat. No. 2,129,692 to E. J. Hottinger the selector assembly controls the functioning of the alignment assembly both directly and indirectly. The segmented selector assembly directly controls the alignment assembly by means of a finger disposed within recessed grooves in the alignment assembly. A spring-bias torsion force rotates the alignment assembly, the alignment of the preselected detonator in the fuze explosive train determined by the arc length of the groove in which the finger is disposed. Indirect control of the alignment assembly is exerted through a group of spring-biased elements, one of the control elements functioning under setback force to retract the firing pin from a recess in the alignment assembly, freeing it to rotate to align the selected detonator in the fuze explosive train.
In U.S. Pat. No. 1,863,888 to A. Varaud the alignment assembly is stationary. In lieu of a PD detonator there is an obturated firing passage connecting the impact primer with the explosive detonator. The delay charge is parallel to the firing passage and interconnected thereto by a perpendicular passage. The primer reaction energy, therefore, must be transmitted through two ninety degree turns to ignite the delay charge. Reaction energy is attenuated when it is transmitted through passages which are not approximately straight; the delay passage configuration of the Varaud fuze, therefore, decreases the probability that the primer reaction energy will be sufficient to ignite the delay charge. The selector assembly indirectly controls the alignment assembly by controlling the retraction of a spring-biased plunger from a centrifugal bolt which obturates the firing passage. Centrifugal force radially displaces the spring-biased centrifugal bolt, thereby withdrawing the obturating member from the firing passage so that the reaction energy of the primer travels in a straight line to the explosive detonator.